Low density/high strength materials are used in subsea industries in a wide variety of applications. The primary purpose of the materials is to lend buoyancy and/or thermal insulation to equipment and structures to reduce load and/or minimize heat loss. The material of choice for this purpose is epoxy and glass microsphere-based syntactic foam. The epoxy provides strength to withstand the extreme pressures subsea. The hollow glass microspheres provide buoyancy and insulative value.
This material and the processes used to manufacture and convert these materials into buoyant/insulative objects have remained essentially unchanged for over 50 years. The most common process consists of mixing epoxy resins with hollow glass microspheres (also known as microballoons), dispensing this mixture into molds or rotationally-molded plastic housings and then curing. In some cases, to increase buoyancy and/or insulative value further, macrospheres (also known as minispheres, 0.2″-2.0″ in diameter) are added to the molds or housings and the syntactic foam is poured around them. In almost all cases, secondary manufacturing processes are necessary to complete the objects.
Since the applications for these materials vary widely, innumerable sized and shaped forms must be created. Custom tooling must almost always be produced to cast the parts. This is an expense and also adds time to each project.
There are numerous drawbacks to this existing material and methodology which have yet to be overcome. A first drawback is that the bulk processing methodology relies on random arrangement of both microspheres and/or macrospheres (both of which contain a distribution of sizes) to create voids within the epoxy. As such, theoretical maximum packing of voids is never achieved. For example, an object with regularly-sized spheres, carefully packed, can achieve a void density of 74%. Maximum void density achieved by random packing of microspheres yields approximately 64%. With the addition of macrospheres to the syntactic foam, void density can be increased further but will never result in optimum sphere packing.
A second drawback is that the spheres are permitted to touch one another or have only a minimum thickness of epoxy between them. Ideally, there would be a carefully calculated thickness of epoxy between each void space to maximize composite strength and insulative value, and minimize density.
A third drawback is that random packing and batch processing technology allows for areas of castings to be void of epoxy. These spaces have microspheres or macrospheres that are not properly encapsulated in epoxy, resulting in weak sections in the objects.
Needs exist for improved subsea buoyancy and insulation materials and processes to meet the challenging demands of subsea applications.